The present invention relates to a pneumatically operated valve for controlling supply of a fluid to a certain apparatus adapted to be operated for an intended purpose using the thus supplied fluid, and more particularly to improvement of or relating to a pneumatically operated valve of the type in which a flow passage of fluid is normally kept in the opened state or in the closed state by means of a valve portion of the piston rod under the effect of a force exerted on the piston in a predetermined direction and. When any abnormal fluctuation of pressure of fluid is detected, pressurized air is introduced into the interior of the casing so as to allow its pressure to act on the piston against the aforesaid force so that the flow passage is shifted from the opened state to the closed state or from the closed state, to the opened state whereby both a normally opened type pneumatically operated valve and a normally closed type pneumatically operated valve can be constituted using parts and components having the same shape and dimension, merely by changing the direction of assembling of a certain member.